Electric machines are utilized in a wide variety of applications. For example, hybrid/electric vehicles (HEVs) typically include an electric traction drive system that includes an alternating current (AC) electric machine which is driven by a power converter with a direct current (DC) power source, such as a storage battery. Machine windings of the AC electric machine can be coupled to inverter sub-modules of a power inverter module (PIM). Each inverter sub-module includes a pair of switches that switch in a complementary manner to perform a rapid switching function to convert the DC power to AC power. This AC power drives the AC electric machine, which in turn drives a shaft of the HEV's drivetrain.
As used herein, the term “multi-phase” refers to two or more phases, and can be used to refer to electric machines that have two or more phases. A multi-phase electric machine typically includes a multi-phase PWM inverter module that drives one or more multi-phase AC machine(s). One example of such a multi-phase electric machine is a three-phase AC machine. In a three-phase system, a three-phase pulse width modulated (PWM) inverter module drives one or more three-phase AC machine(s). For example, some traditional HEVs implement two three-phase PWM inverter modules and two three-phase AC machines (e.g., AC motors) each being driven by a corresponding one of the three-phase PWM inverter modules that it is coupled to.
In many systems, the inverter modules are driven by switching vector signals that are generated based on voltage command signals. The voltage command signals are generated based on current command signals that are provided from a torque-to-current mapping module. In such systems, the torque-to-current mapping module receives a torque command signal (Te*), an angular rotation speed (ωr) of the machine, and a DC input voltage (VDC) as inputs, and maps these inputs to current commands that will ideally cause the machine to generate the commanded torque (Te*) at a given machine speed (ωr).
A conventional torque-to-current mapping module is implemented using a set of lookup tables (LUTs). These LUTs are typically stored in read-only memory (ROM), which is a limited memory resource in many electric machine drive systems. As such, one drawback associated with the conventional torque-to-current mapping module is that the LUTs require a significant amount of memory resources, which can, in some cases, exceed the amount of memory available.
It would be desirable to provide improved methods, systems and apparatus for generating current commands used to control a multi-phase electric machine. It would also be desirable to provide improved methods, systems and apparatus for mapping torque commands to current commands that consume less memory resources. Other desirable features and characteristics of the present invention will become apparent from the subsequent detailed description and the appended claims, taken in conjunction with the accompanying drawings and the foregoing technical field and background.